Zinc oxide is currently employed widely in optoelectronic devices. Wurtzite ZnO is an intrinsic n type semiconductor because of deviation from stoichiometry. The natural oxygen vacancies (anionic sites) lead to a redistribution in the occupation of the anionic sites by cationic species, in this case Zinc, as interstitials. These two types of defects lead to donor levels situated at about 0.05 eV from the conduction band.
It has already been attempted to eliminate these defects to obtain p doped ZnO. A procedure consisting of a co-doping with Ga acting as donor and N as acceptor is described in M. Joseph et al., “p-type Electrical Conduction in ZnO Thin Films by Ga and N Codoping”, Jpn. J. Appl. Phys., Vol. 38 (1999), pp L 1205–L 1207. The article by T. Yamamoto et al. entitled “Solution Using a Co-doping Method to Unipolarity for the Fabrication of p-type ZnO”, published in the journal Jpn. J. Appl. Phys., Vol. 38 (1999), pp. L 166–L 169, also employs this codoping method.
U.S. Pat. No. 4,904,618 proposes a procedure for doping wide bandgap semiconductors such as ZnSe or ZnTe. This procedure consists of incorporating a pair of primary and secondary dopants in the crystal (for example, N and Li, respectively), and then eliminating the most mobile of the two.
A difficulty in these techniques is in controlling the incorporation mechanisms of the constituents to obtain a chemical composition of the growth front conducive to an appropriate stoichiometry of the epitaxial crystal.
It would, therefore, be advantageous to simplify these known procedures.